1. Field of the Invention
The present invention relates, in general, to metal making apparatus and processes and, more specifically, to metal making apparatus and processes utilizing a tundish as an intermediate receptacle to transfer molten metal from a ladle to a continuous metal casting machine.
2. Description of Relevant Art
In metal making processes, such as steel making, molten metal is transferred from a furnace via a ladle to a casting machine. When a continuous casting machine, such as a continuous slab caster, is employed, a sufficient quantity of molten metal must be maintained to supply the continuously operating slab caster. Receptacles known as "tundishes" are employed to receive molten metal from one or more ladles. A discharge nozzle is formed in the bottom wall of the tundish opening to the continuous slab caster. In this way, a sufficient quantity of molten metal is maintained within the tundish to supply a continuous stream of molten metal to the continuous slab caster.
However, in all metal making processes and, in particular, steel making processes, a layer of slag containing metal impurities forms above the top surface of the molten metal within the ladle and the tundish. When the molten metal is discharged from the tundish, it is necessary to maintain a separation between the slag and the molten metal so that high quality steel without significant amounts of slag may be produced.
Since the slag forms a layer of impurities several inches thick on top of the layer of molten metal in the tundish, slag may be introduced to the continuous slab caster through the discharge nozzle of the tundish when the level of molten metal drops below a predetermined level. When this critical level of molten metal is reached, slag is introduced directly through the discharge nozzle of the tundish into the casting machine.
In addition, the flow of molten metal through the discharge nozzle in the tundish creates a vortex which introduces a conically-shaped rotation to the molten metal within the tundish immediately above the discharge nozzle. When a sufficient quantity of molten metal is maintained within the tundish, the vortex forms completely within the molten metal layer and does not reach to the slag layer atop the molten metal layer. However, when the level of molten metal within the tundish is below the predetermined critical depth, the vortex reaches into the slag layer and draws slag through the center of the vortex to the discharge nozzle along with the molten metal. This causes the introduction of slag into the molten metal in the caster and results in steel having less than desirable qualities.
Thus, in order to prevent the production of steel having less than desirable qualities, such as that caused by the introduction of significant amounts of slag into the steel, it is necessary that the level of molten metal in the bottom of the tundish be maintained above the predetermined critical level. This requires measurement of the depth of the molten metal layer in the tundish. Previously, measurement sticks had been inserted through an access hole in the cover of the tundish to the bottom of the tundish. When the measuring stick is withdrawn, the depth of the molten metal layer may be easily determined. However, measurement of the depth of the molten metal layer must be repeated on a nearly continuous basis since molten metal is constantly being supplied to the tundish by ladles and continuously discharged through the discharge nozzle of the tundish to the continuous caster. This technique is therefore subject to considerable error and there is always a high possibility of the formation of steel having less than desired qualities if the level of molten metal inadvertently drops below the predetermined critical level.
Various apparatus have also been devised to inhibit or minimize the vortex formed above the discharge nozzle of the tundish to prevent the mixing of slag and molten metal at the discharge nozzle site. U.S. Pat. No. 4,601,415 discloses a buoyant polygonal body having a weighted apex. The body floats at the molten metal/slag interface and is held above the discharge nozzle in the vortex. The body due to its mass inhibits the formation of the vortex and minimizes the overall size of the vortex to prevent mixing of the slag with the molten metal. However, while this device minimizes or inhibits the formation of the vortex above the discharge nozzle in the tundish, it does not provide any type of measurement of the level of molten metal at the bottom of the tundish.
Thus, it would be desirable to provide an apparatus for measuring the depth of the molten metal layer in the bottom of a tundish or other molten metal receptacle which overcomes the problems of previous measurement apparatus. It would also be desirable to provide such a measurement apparatus which is inexpensive in cost and, at the same time, easy to use. It would also be desirable to provide such a measurement apparatus which provides an indication of the depth of the molten metal layer in the bottom of a tundish or other molten metal receptacle which does not require access by an operator to the interior of the tundish or molten metal receptacle.